Wednesday, May 21, 2014

Aptina's patent application US20140125838 "Imaging systems with modified clear image pixels" by Jeffrey Mackey, Gershon Rosenblum, and Alexandre Dokoutchaev proposes an improvement over the previously published Clarity+ application. The necessity for the improvement is explained as: "Some imaging systems replace the green color filters in the standard Bayer mosaic pattern by a non-absorbing clear material. This type of clear pixel can boost the sensor light sensitivity by a factor of more than two, thereby significantly improving the medium and low-light performance. However, this type of color scheme is partially subtractive and therefore can require the use of relatively high color correction coefficients. In addition, the high sensitivity of the clear pixel can result in a color channel imbalance that is typically corrected using relatively high white-balance coefficients. Thus, if care is not taken, proper color correction using these types of color correction and white-balance coefficients can result in an enhancement of pixel noise."

The solution is to modify the clear pixel: "Image pixels 190 may include modified clear pixels. For example, some of pixels 190 may include color filter elements formed from transparent material with a color additive such as a yellow pigment or other similarly shaded pigment or dye. The pigment may be added to the transparent color filter element material in concentrations configured to give desired spectral filtration qualities to an otherwise uniformly transparent color filter array pixel."

The processing pipeline with Clear pixel modified into Yellow is quite similar to the original, where C (clear) is changed to Y: